The present invention relates to a negative-working photoresist composition or, more particularly, to a chemical-amplification negative-working photoresist composition suitable for use in the photolithographic patterning works in the manufacture of various electronic devices, which has high transparency to the ArF excimer laser beams for pattern-wise exposure and is capable of giving a finely patterned resist layer with high pattern resolution along with little swellability of the resist layer in the developer solution and excellently orthogonal cross sectional profile of the patterned resist layer.
As is disclosed in Japanese Patent Publication 8-3635 and elsewhere, the basic formulation of a chemical-amplification negative-working photoresist composition is known, which comprises a radiation-sensitive acid-generating agent, an alkali-soluble resin such as novolak resins, polyhydroxystyrene resins and the like and an amino resin such as melamine resins, urea resins and the like in combination and in which the alkali-soluble resinous ingredient in the exposed areas of the resist layer is rendered alkali-insoluble in the presence of the acid generated from the acid-generating agent. Namely, a crosslinking reaction proceeds between the alkali-soluble resin and the amino resin by interacting with the acid generated by irradiation with actinic rays to form a pattern-wise latent image of the alkali-insolubilized resin which is developed with an alkaline developer solution to dissolve away the resist layer in the unexposed areas leaving a negatively patterned resist layer in the exposed areas.
The chemical-amplification negative-working photoresist composition of the above described type comprising an acid-generating agent, alkali-soluble resin and amino resin is quite satisfactory for use in the photolithographic process in which the exposure light is the i-line ultraviolet light or KrF excimer laser beam of 248 nm wavelength. As a trend in recent years, however, it is desired to employ an exposure light of a shorter wavelength such as ArF excimer laser beams in order to comply with the requirement for finer and finer patterning in the manufacture of semiconductor devices of higher degrees of integration, for which the photoresist composition of the above described type cannot be quite satisfactory.
Various proposals have been made heretofore for chemical-amplification negative-working photoresist compositions suitable for the photolithographic patterning work using ArF excimer laser beams as the exposure light, referred to as an ArF resist hereinafter, including (1) those comprising a resinous base ingredient derived from a copolymer of 5-methylenebiscyclo[2.2.1]-2-heptane and maleic acid by esterifying one of the carboxyl groups of the maleic acid moiety, an aliphatic cyclic polyhydric alcohol as the cross-linking agent and an acid-generating agent disclosed in Journal of Photopolymer Science and Technology, volume 10, No. 4, pages 579–584 (1997), (2) those comprising a resinous base ingredient which is a copolymer of a first acrylic acid ester having an epoxy group-containing cyclic hydrocarbon group in the ester portion of the molecule and a second acrylic acid ester having a carboxyl group-containing cyclic hydrocarbon group in the ester portion of the molecule in combination with a crosslinking agent and an acid-generating agent which are each the same one as mentioned above disclosed in Journal of Photopolymer Science and Technology, volume 11, No. 3, pages 507–512 (1998) and (3) those comprising a resinous base ingredient which is a copolymer of a first acrylic acid ester having a hydroxyl group-containing cyclic hydrocarbon group in the ester portion of the molecule and a second acrylic acid ester having a carboxyl group-containing cyclic hydrocarbon group in the ester portion of the molecule in combination with a crosslinking agent and an acid generating agent which are each the same one as mentioned above disclosed in SPIE Advances in Resist Technology and Processing XIV, volume 3333, pages 417–424 (1998).
The feature of the above described ArF resists is that, in order to increase the transparency of the base resin to the ArF excimer laser beams and to obtain alkali-solubility of the resin, the resin is modified by introducing carboxyl group-containing polycyclic hydrocarbon groups susceptible to crosslinking and by introducing epoxy groups and alcoholic hydroxyl groups into the resin so as to enhance crosslink-ability.
Although, in the ArF resist compositions of the above described types, a negatively-patterned resist layer can be formed by the crosslinking reaction of the resinous ingredient and the crosslinking agent in the presence of an acid generated by irradiation with ArF excimer laser beams by virtue of the ester or ether linkages, the resist composition in the exposed areas still contains remaining uncrosslinked carboxyl groups and alcoholic hydroxyl groups so that the resist layer in the exposed areas becomes swollen more or less in the development treatment with an alkaline developer solution undesirably resulting a patterned resist layer having round shoulders in the cross sectional profile not to ensure high quality of the patterned resist layer.